Facial recognition systems commonly use visual acquisition and algorithms to identify or authenticate a person by analyzing certain facial features (such as relative position of nose, eyes, jaw and others) and comparing against a reference or samples within a database. They are most commonly implemented using an image or video feed in conjunction with a computing system executing an identification algorithm. They can be used standalone or in conjunction with other biometrics such as retina/iris and fingerprint scanning. The trend in smartphones is to add facial recognition to authentication functions as an alternative or in addition to personal identification number (PIN) codes and/or fingerprint. Such systems often use a two-dimensional (2D) camera to acquire the facial information, but a 2D only system is easy to defeat with a still picture. Even when using added levels of security (e.g. requirement to blink one eye during recognition) such systems are usually not robust and secure enough to replace other biometric sensors.